1. Field of the Invention
The present invention relates to a polarizing plate, a method for producing the polarizing plate, and a liquid crystal display device. In particular the present invention relates to a polarizing plate, a method for producing the polarizing plate, and a liquid crystal display device that can be manufactured with high productivity, that can utilize light emitted from a light source with high efficiency, and that contributes to manufacture of a large display screen.
2. Description of the Related Art
A liquid crystal display device comprises a liquid crystal panel and a backlight device that illuminates this liquid crystal panel from a backside. The backlight device comprises a light reflective element, a plurality of light sources and a light diffusion plate in this order. For such light sources, a fluorescent lamp comprising a plurality of fluorescent materials having a light emission peak at wavelength regions at which humans have high color sensitivity (in particular, wavelengths at around 450, 540 and 610 nm) (i.e., a three band tube) has been widely used. In recent years, a fluorescent lamp further comprising a fluorescent material having another light emission peak at a wavelength in a region longer than 610 nm in addition to the fluorescent materials having the peaks at the conventional three wavelength regions (i.e., a four band tube) has been studied. Such a fluorescent lamp has an advantage in an enhanced color reproducibility of displayed images. However, such a lamp also has a disadvantage in high cost per one fluorescent lamp, which leads to high production cost of the entire backlight device. In recent years, there is a demand for reducing electric power consumption (energy saving) of the backlight device in terms of environmental protection, and it has been considered to reduce the number of the fluorescent lamps for use.
Under such a circumstance, in order to reduce the production cost elevation and to reduce the number of the fluorescent lamps for use aiming at energy saving, it is being practiced to dispose a brightness enhancement film on the light diffusion plate for compensating the reduced number of the fluorescent lamps. The brightness enhancement film is a member that can enhance display brightness on the liquid crystal display device. As examples therefor, Patent Documents 1 to 3 discloses those containing a linearly-polarized light separation element that allows a specific linearly-polarized light to pass therethrough and reflects a light that is linearly-polarized in an orthogonal direction with respect to the specific light.
The liquid crystal panel used in the liquid crystal display device comprises a liquid crystal cell and two linear light polarizing films that sandwich this liquid crystal cell and are disposed in a crossed Nicol pattern. Such a linear light polarizing film is usually manufactured by absorption of iodine or a dichroic dye by a polyvinyl alcohol film which is stretched in a lengthwise direction. Thus, the linear light polarizing film absorbs the light that is linearly-polarized along the film's lengthwise direction, whereas the film transmits the light that is linearly-polarized along the film's crosswise direction.    Patent Document 1: JP-Hei09-506837 A    Patent Document 2: JP-Hei11-509331 A (corresponding to U.S. Pat. No. 7,423,708)    Patent Document 3: JP-Hei09-507308 A (corresponding to U.S. Pat. No. 6,096,375)